1. Field of the Invention
The present invention relates to a broadband wireless access system, and more particularly, to a method for a mobile station to save power for prescribed duration without performing a paging procedure and apparatus therefor.
2. Discussion of the Related Art
In the following description, an idle mode of a mobile station and a paging group are schematically explained.
First of all, when a mobile station moves in a radio link environment constructed with multiple base stations, an idle mode is an operation of supporting DL (downlink) broadcast traffic reception to be periodically performed without registration with a specific base station.
When a mobile station fails to receive traffic from a base station for predetermined duration, it is able to enter an idle mode for power saving. Having entered the idle mode, the mobile station receives a broadcast message (e.g., a paging message) sent by the base station in an available interval and is then able to determine whether to enter a normal mode or stay in the idle mode. Moreover, the mobile station in the idle mode performs a location update to inform a paging controller of its location.
An idle mode gives a benefit to a mobile station in a manner of eliminating a request for activation associated with a handover and general management requests. The idle mode puts limitation on mobile station activity in a manner of enabling a mobile station to perform a scan in a discrete cycle only. Therefore, the idle mode saves power and operational resources used by the mobile station.
An idle mode provides a simple and appropriate method of informing a mobile station of pending downlink traffic and removes a radio interface and network handover (HO) traffic from an inactive mobile station, thereby giving benefits to a network and a base station.
Meanwhile, a paging means a function of obtaining a location (e.g., a prescribed base station, a prescribed switching center, etc.) of a mobile station corresponding to an incoming signal occurrence in mobile communication. A plurality of base stations (BSs) supporting the idle mode can configure a paging area by belonging to a specific paging group.
In this case, the paging group indicates a logical group. The object of the paging group is to provide an adjacent range area that can be paged in downlink (DL) if there is a traffic targeting a mobile station (MS). Preferably, the paging group is large enough to enable a specific mobile station to exist within the same paging group for the most of time and is also small enough to enable a paging load to maintain an appropriate level.
A paging group can include at least one base station. And, one base station can be included in at least one or more paging groups. A paging group is defined by a management system. A paging group is able to use a paging group-action backbone network message. A paging controller manages a list of mobile stations in idle mode using a paging-announce message that is one of backbone network messages. And, the paging controller is able to manage initial paging of all base stations belonging to a paging group.
In order to increase a rate of successful paging, a mobile station is able to perform a location update procedure. In this case, a location update is an action of a mobile station to increase a hit rate of paging performed on a mobile station having entered an idle mode and indicates a procedure for a mobile station to report a newly entered location or region in moving into a new region. This location update procedure can be performed in a manner that a mobile station and a base station exchange a ranging request (RNG-REQ) message and a ranging response (RNG-RSP) message with each other.
In the following description, one example for a procedure for a mobile station to enter an idle mode and operate in the general IEEE 802.16 system is explained with reference to FIG. 1.
Referring to FIG. 1, first of all, a mobile station is able to send a deregistration request (hereinafter abbreviated DREG-REQ) message to a serving base station to enter an idle mode from a normal mode [S101].
Having received the DREG-REQ message, the serving base station can exchange information on the mobile station and information on itself with a paging controller. IN particular, the serving base station is able to inform the paging controller of a mobile station identifier of the mobile station entering an idle mode and a corresponding serving base station identifier. And, the paging controller is able to inform the serving base station of a paging group ID (PGID) or a paging controller ID (PCID). The paging group ID or the paging controller ID is usable in transmitting and receiving a paging message [S102].
Subsequently, the serving base station is able to transmit a deregistration command (hereinafter abbreviated DREG-CMD) to the mobile station. The serving base station is able to send a deregistration command (MOB_DREG-CMD) message to the mobile station in response to the deregistration request message. In this case, the deregistration command message can contain paging information therein. And, the paging information can include such a parameter as a paging cycle, a paging offset, a paging listen interval and the like. Moreover, the deregistration command message can further contain a paging controller ID and a paging group ID [S103].
Having received the DREG-CMD message from the serving base station, the mobile station checks that the idle mode entry request has been successfully granted and is then able to enter the idle mode. Based on the paging information carried on the MOB_DREG-CMD message, the mobile station is able to receive the paging message. In particular, the mobile station is able to monitor a radio channel during the paging listen interval to check whether there is a paging message to be delivered to itself. For the rest of time, the mobile station operates in a sleep mode or a radio turn-of mode to save power consumption [S104].
A call for the mobile station or an external packet can be inputted to the paging controller [S105].
The paging controller can correspondingly perform a paging procedure for detecting a mobile station. In doing so, the paging controller is able to deliver a paging announcement message to all the base stations within a paging group [S106].
Subsequently, each of the base stations having received the paging announcement message within the paging group can broadcast a paging advertisement (MOB_PAG-ADV) message to every mobile station managed by the corresponding base station [S107].
Having received the paging advertisement message from the serving base station, the mobile station checks the received message. If the mobile station is paged, the mobile station enters a normal mode and is then bale to perform communication with the serving base station [S108, S109].
However, in the general IEEE 802.16 based wireless communication system, a mobile station has to enter an idle mode to save power despite that a paging procedure is unnecessary. So, paging relevant information is unnecessarily allocated to the mobile station. Thus, although the mobile station in the idle mode needs not to receive a paging message, the mobile station should wake up to cope with a paging interval.